java - 查找二维数组的标准差

Question

我正在努力寻找我的作业的标准差，我已经做了其他所有事情，但我只是在最后一点上挣扎。简而言之，我的作业问题是:我收到了一组学生作业结果的文本文件(必须是任意数量的)。给出的唯一数据是学生姓名、粉丝和他们的成绩，您需要计算他们的平均成绩和标准差。输出应如下所示:

Student Name     FAN      Part 1 Part 2 Part 3 Part 4 Mark    Grade
Adam Adamson     adam0001 85.4   79.8   82.4   86.1   82.77%  DN
Bethany Bright   brig0001 89.7   85.6   84.2   82.9   84.92%  DN
Cameron Carlson  carl0001 55.45  49.82  60.4   42.27  50.23%  P
David Dawson     daws0001 72.6   78.49  80.2   65.88  74.46%  CR
Evelyn Ellis     elli0001 50.2   35.88  48.41  58.37  46.57%  FA
Frances Fitz     fitz0001 78.9   75.67  82.48  79.1   78.38%  DN
Greg Gregson     greg0001 24.3   32.88  29.72  28.4   30.05%  F
Harriett Hope    hope0001 52.2   58.93  61.5   63.44  60.12%  P
Ivan Indigo      indi0001 88.4   91.23  90.05  92.46  91.08%  HD
Jessica Jones    jone0001 82.33  89.74  81.3   84.85  85.84%  HD
                  Average 67.948 67.804 70.066 68.377 68.44%  CR
                                               StdDev 19.4442

我知道我需要使用的方程，我知道我需要使用哪些数字，但我只是不知道如何获得它们。我将向您展示我需要做什么，希望您能进一步理解我的代码:

the total of the averages divided by 10 = 68.442

sum = (82.77-68.442)^2 + (84.92-68.442)^2 + (50.23-68.442)^2 + ... + (85.84-68.442)^2
StdDev = Math.sqrt(sum/10)

stdDev = 19.4442

我为此使用了 3 个类，我的主类主题管理，一个学生类，其中包含一个包含学生姓名和粉丝的数组(两者都与我的问题无关，但我认为我最好只是设置场景)，最后是 StudentsMarks 类，其中包含下面显示的我的 StdDec 方法:

public static double StdDev() throws IOException
{
    String [][] marks = StudentMarks.StudentMarks();

    double mean = 0, average = 0, stdDev = 0;
    int row = 0;
    for(row = 0; row < marks.length; row++)
    {                                          //ROW,COL
        double score1 = Double.parseDouble(marks[row][2]);  //parsing the data from the array into a double
        double score2 = Double.parseDouble(marks[row][3]);
        double score3 = Double.parseDouble(marks[row][4]);
        double score4 = Double.parseDouble(marks[row][5]);

        average = score1*0.1 + score2*0.4 + score3*0.2 + score4*0.3;   

        mean = average/row;
        stdDev = Math.sqrt(Math.pow(average - mean,2)/row);   
    }  
    return stdDev;
}

Answer 1

你需要 2 个循环，因为你需要从每一行中减去平均值。

double[] sum = new double[marks.length];

for(row = 0; row < marks.length; row++)
{                                          //ROW,COL
    double score1 = Double.parseDouble(marks[row][2]);  //parsing the data from the array into a double
    double score2 = Double.parseDouble(marks[row][3]);
    double score3 = Double.parseDouble(marks[row][4]);
    double score4 = Double.parseDouble(marks[row][5]);

    sum[row] = score1*0.1 + score2*0.4 + score3*0.2 + score4*0.3;   
    average += sum[row];
}
average = average/sum.length; //1
for(row = 0; row < sum.length; row++)
{
        mean += Math.pow(Math.abs(sum[row] - average),2);           
}
mean = mean/marks.length;//2
stdDev = Math.sqrt(mean);